CARACTERIZACIÓN PETROGRÁFICA, GEOQUÍMICA Y EDAD DE LA SIENITA NEFELÍNICA DE SAN JOSÉ DEL GUAVIARE
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Universidad Industrial de Santander
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Las rocas de la Sienita Nefelínica de San José del Guaviare se presentan como dos cuerpos a unos 20 km al SW del municipio San José del Guaviare. Vesga y Castillo (1972) reportan el primero de ellos en la vereda La Pizarra, otro cuerpo del cual no se tenían referencias bibliográficas aparece en la vereda Las Delicias. Petrográficamente las rocas son sienitas nefelínicas, monzosienitas nefelínicas y granofels de feldespato y nefelina constituidas por microclina, nefelina, plagioclasa ± biotita ± arfvedsonita como minerales principales y como minerales accesorios fluorita, esfena, apatito, granate, circón, epidota y calcita. Las rocas presentan un carácter mixto de texturas y estructuras ígneas en el cuerpo La Pizarra y metamórficas heredadas (restitas) que predominan en el cuerpo Las Delicias, permitiendo sugerir un ambiente de formación a partir de procesos de anatexia. Las rocas geoquímicamente muestran una naturaleza alcalina, localizándose dentro del campo de rocas formadas en ambiente de intraplaca.Se determinó por los métodos U/Pb en circón y 40Ar/39Ar (HS) en biotita una edad de 577.8 ± 6.3 - 9 Ma (Ediacaran) de cristalización y 494±5 Ma (Furoginiano) de enfriamiento.
Palabras clave: Sienita nefelínica, San José del Guaviare, Anatexia, Alcalino.
The San José del Guaviare Nepheline Syenite includes two rock bodies that crop out 20 km SW of the town with the same name. The first of these bodies, which had already been reported by Vesga and Castillo (1972), is exposed in the La Pizarra area. The second body, which had not been previously reported, occurs in the Las Delicias area.Petrographic characterization shows that rocks correspond to nepheline syenite, nepheline monzosyenite, and feldspar + nepheline granofels. The main minerals in the rocks are microcline + nepheline + plagioclase ± biotite ± arfvedsonite, and accessory phases include fluorite, sphene, apatite, garnet, zircon, epidote and calcite. Structures and textures are chiefly igneous in the la Pizarra body and mainly metamorphic (restitic) in the Las Delicias body. The geochemical character of the rocks is alkaline, and they correspond to within- the field of rocks formed in intraplate environment. The above features suggest that the San José del Guaviare syenite was formed by anatexis in a continental environment.U/Pb dating of zircon and 40Ar/39Ar (HS) dating of biotite indicates age 577.8± 6.3 - 9 Ma (Ediacaran) crystallization and 494±5 Ma (late Cambrian) cooling. Keywords: Nepheline syenite, San José del Guaviare, Anatexis, Alkaline magmas.
The San José del Guaviare Nepheline Syenite includes two rock bodies that crop out 20 km SW of the town with the same name. The first of these bodies, which had already been reported by Vesga and Castillo (1972), is exposed in the La Pizarra area. The second body, which had not been previously reported, occurs in the Las Delicias area.Petrographic characterization shows that rocks correspond to nepheline syenite, nepheline monzosyenite, and feldspar + nepheline granofels. The main minerals in the rocks are microcline + nepheline + plagioclase ± biotite ± arfvedsonite, and accessory phases include fluorite, sphene, apatite, garnet, zircon, epidote and calcite. Structures and textures are chiefly igneous in the la Pizarra body and mainly metamorphic (restitic) in the Las Delicias body. The geochemical character of the rocks is alkaline, and they correspond to within- the field of rocks formed in intraplate environment. The above features suggest that the San José del Guaviare syenite was formed by anatexis in a continental environment.U/Pb dating of zircon and 40Ar/39Ar (HS) dating of biotite indicates age 577.8± 6.3 - 9 Ma (Ediacaran) crystallization and 494±5 Ma (late Cambrian) cooling. Keywords: Nepheline syenite, San José del Guaviare, Anatexis, Alkaline magmas.